Such a filling head is described in French Patent No. 2 095 562, which discloses a closure element for a control valve, an electrovalve acting in the region of the feed orifice for the circulation chamber, and comprising a mechanical obturator in the form of a piston sliding in the body of the filling head, either towards a closure position of the feed orifice under the action of an electro-magnet, or towards an open position of this feed orifice under the action of a return spring.
Because of the control of the stopping of the passage of filling liquid towards the bottle by detection of a liquid level in the latter, this known filling head ought to permit filling of bottles to a rigorously constant level, determined by the level of the detection means for a predetermined level of each bottle in the course of filling.
Nevertheless, this known filling head has a certain imprecision in the final effective filling level of each bottle, because of the positioning of the closure element of the controlled valve in the region of the feed orifice of the circulation chamber, and because of the structure of this closure element of the control valve. The positioning of the closure element of the control valve disclosed in the French Patent No. 2 095 562 results in the fact that, when this element reaches its position of closure of the feed orifice of the circulation chamber after the filling liquid in the bottle has reached the level of the detection means and these means have emitted a corresponding control signal, found between this closure element of the controlled valve and a zone of the lower end of the discharge tube extending inside the bottle, and this volume can be more or less discharged into the bottle after the instant at which the closure element of the controlled valve has reached its closed position. As a result, this instant does not necessarily coincide with the actual instant of stopping of discharge of the filling liquid into the inside of the bottle, and the level finally reached in this latter by the filling liquid can more or less pass, in an uncontrollable manner, the level of the detection means; this results in a first factor for imprecision of the level effectively reached in the bottle, by the filling liquid, at the end of filling. The structure chosen for the closure element of the controlled valve makes it necessary to provide sealing means with respect to the outside, both in the region of the connection between the obturator and the electromagnet, and in the region of the connection between the obturator and the return spring, which necessarily leads to a more or less controllable retardation of the movement of the obturator towards its position of closure of the feed orifice for the circulation chamber from the instant where the level of the liquid in the bottle being filled has reached the detection means, and where these detection means have emitted a corresponding control signal. From this, the arrival of the obturator in the closure position of the feed orifice for the circulation chamber is retarded, in an undetermined manner, with respect to the effective arrival of the level of the liquid in the bottle at the level of detection means.
Further, because of its structural complexity, particularly in the region of the closure element of the controlled valve, the filling head recommended in French Patent No. 2 095 562 is not hygienic, because it has numerous recesses constituting zones for accumulation and possible development of germs and bacteria and zones which are difficult to clean by circulation of cleaning liquid, i.e., in accordance with the normal method used for cleaning machines for automatic filling of bottles.